Helen was a suborbital rocket, designed for Google Lunar X Prize, to serve as avionics and propulsion testbed. It also provided ARCA with extraordinary knowhow in order to prepare and operate large vehicles in close cooperation with the Navy, Air Force and Civil Aviation.

The Helen rocket was built in two versions. The first version was a three stage rocket launched from a solar balloon. The second version Helen 2, had spherical fuel tanks and it was launched from a helium balloon.

The first launch attempt took place on November 14, 2009 during Mission 3. The rocket launch procedure was carried out successfully, but the 7,060,000 ft3 (200,000 m3) balloon inflation, directly on the sea surface, wasn't properly performed. The balloon envelope was entangled with the inflation tubes. ARCA and Navy divers' efforts to untangle the balloon proved successful after six hours, but because of the winter season, the sun was near sunset. Since a solar balloon was used and the envelope couldn't be heated by the sun, the launch was canceled.

Helen rocket launch attempt was the most complex operation carried by ARCA to date, with the participation of two large Navy ships, and three naval special forces boats. Although the launch involved numerous forces and the cooperation with various military and civilian institutions, ARCA successfully coordinated the activity.

Mission 5

In order to test the Helen rocket avionics (radio/satellite command/telemetry parameters and the live video transmission), ARCA performed Mission 5. The Helen capsule was lifted to an altitude of 17,000 ft (5200 m) by a manned hot air balloon. The maximum distance between the carrier balloon and the command center was 42 km, which corresponded with Helen rocket safety zone.

The mission results were:
- the TV system worked well, the video signal being received for about 90% of total emission time;
- radio and satellite telemetry systems worked perfectly during flight;
- two, out of three command systems worked perfectly, both on satellite and radio. The third on radio, failed.

The Helen 2 version was a two stage rocket, built with spherical fuel tanks, but using the same engines, avionics and payload as initial version.The use of spherical tanks was possible because the vehicle was launched from stratosphere; therefore the aerodynamic drag was low.

Helen 2 technical data

First stage length

11.9 ft

3,6 m

First stage diameter

3,6 ft

1.1 m

Empty weight

352 lb

160 kg

Launch weight

1850 lb

840 kg

First stage vacuum thrust

3,500 lbf

1,600 kgf

Max. speed

3,900 ft/s

1,200 m/s

Max. altitude

260,000 ft

80,000 m

Fuel

HP 70%

HP 70%

Stages

1+2

1+2

Missions 4 & 4B

First launch attempt took place during Mission 4, but the helium carrier balloon ruptured, because of constructive imperfections. A new launch attempt, using a new balloon, took place during Mission 4B. The rocket was launched this time with only one stage. Balloon ascent took 40 minutes to an altitude of 46,000 ft (14,000 m). The flight data were transmitted to the command centers of ARCA and Civil Aviation.
At that altitude the rocket was separated from the balloon and the engine ran for 30 seconds placing the rocket to an altitude of 131,000 ft (40.000 m).

Despite the Navy search efforts, the payload was not recovered. The search was performed in the area where the last telemetry coordinates were transmitted by the Helen capsule. The last transmission was received from an altitude of 4900 ft (1500 m). Analyzing the transmitted data it was decided that the capsule descended with unusual high speed, meaning that the parachute probably did not open, the capsule being destroyed on impact with the water at a speed of 373mph (600 km/h).

The data transmitted by radio and satellite telemetry was properly received, but the high quality footage on board was lost. The live video transmission offered low quality images, because of the cloud cover and the ship movements. In spite of the lack of capsule recovery, this mission was the greatest operational success of ARCA until then. It was also the first and only flight in the Google Lunar X Prize competition, until November 2014.

Vertical rocket stabilization

Helen used a stabilization method without aerodynamic surfaces or RCS, by towing the other rocket stages and the payload. The towing can be made by cables or by rigid articulated system.
In order to have a vertically stabilized rocket, under gravitational field, this method uses the towed mass in the same direction with the thrust. The stabilization effect depends on several elements: the mass of the stabilized body, the mass of the towing body and the length between the stabilized body and the stabilizer body.

This method can be applied in outer space on vertical ascent or descent trajectory under the influence of a gravitational field.
It was used in flight for the first time, with success, during Mission 4B for the Google Lunar X Prize competition.